B.S: I am specifically talking about facebook-unity-sdk-7.7.0 not v 7.3.0
I am using facebook-unity-sdk-7.7.0 and GooglePlayGamesPlugin-0.9.32 in my project. It does not let me build for android and fails with error Unable to convert classes into dex format. See the Console for details.. In Facebook SDK 7.3.0 it works by deleting android support v4, but in 7.7 the same thing does not work.
I had the same problem and this was the way I solved it: Delete the following files from the folder: \ Assets \ FacebookSDK \ Plugins \ Android \ libs: